Your application probably saves its settings in an ini or cfg file. Add a setting for the Languages folder. After first run of the application edit the ini file and change the entry for the Languages folder to point to the "project\i18n" -- this way is is not necessary at all to copy files around.

About Mac, I don't have one. I'm running it on a slow VM. I'm not sure where DefaulTranslator looks for translation on a Mac. Will be nice to know more about it.

I'm not aware of any apps on Mac that use .po files for localization. Most use a combination of .strings and .nib files under the locale's folder (eg, MyApp.app/Contents/Resources/en.lproj for English). GIMP uses .mo files - maybe something similar to .po?

Note that Mac apps generally don't use .cfg, etc. files. Preferences are stored under ~/Library/Preferences, etc. See the list here: